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Question 61 - JN0-636 discussion

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You configure Source NAT using a pool of addresses that are in the same subnet range as the external ge-0/0/0 interface on your vSRX device. Traffic that is exiting the internal network can reach external destinations, but the return traffic is being dropped by the service provider router.

Referring to the exhibit, what must be enabled on the vSRX device to solve this problem?

A.
STUN
Answers
A.
STUN
B.
Proxy ARP
Answers
B.
Proxy ARP
C.
Persistent NAT
Answers
C.
Persistent NAT
D.
DNS Doctoring
Answers
D.
DNS Doctoring
Suggested answer: B

Explanation:

Proxy ARP is a technique used by routers to answer ARP requests on one network segment on behalf of hosts on another network segment. This is useful in situations where a host on one network segment needs to communicate with a host on another network segment, but the two hosts are not directly connected. In this case, the router acts as a proxy, answering ARP requests on behalf of the other host. In the exhibit, the vSRX device is configured to use a pool of addresses that are in the same subnet as the external interface ge-0/0/0 for source NAT. This means that the vSRX device will translate the source IP address of the internal hosts to one of the addresses in the pool before sending the packets to the external network. However, the external hosts will not know how to reach the NATed addresses, since they are not directly connected to the vSRX device. They will send ARP requests for the NATed addresses, expecting to receive a MAC address from the vSRX device. If proxy ARP is not enabled on the vSRX device, it will not respond to these ARP requests, since it does not have the NATed addresses configured on its interface. The ARP requests will time out and the packets will be dropped by the external hosts or the service provider router. To solve this problem, proxy ARP must be enabled on the vSRX device for the NATed addresses. This will allow the vSRX device to respond to the ARP requests from the external hosts, providing its own MAC address as the destination. The external hosts will then send the packets to the vSRX device, which will reverse the NAT and forward the packets to the internal hosts. Reference:

Configuring Proxy ARP (CLI Procedure)

[SRX] When and how to configure Proxy ARP (https://supportportal.juniper.net/s/article/SRXDynamic-

VPN-scenario-for-configuring-Proxy-ARP-on-SRX?language=en_US)

asked 18/09/2024
Fernando Pereira dos Santos
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